In the recent drive for higher integration of ICs, it is desired to form a finer size pattern. When resist patterns with a feature size of 0.2 μm or less are formed by lithography, chemically amplified resist compositions utilizing the catalysis of acid are often used in order to attain a high sensitivity and resolution. Since materials used in chemically amplified resist compositions must have a certain level of transmittance to energy radiation for use in pattern exposure, a suitable one is selected from numerous materials in accordance with the wavelength of energy radiation.
As is well known in the art, chemically amplified positive resist compositions which are commercially implemented at the present are developed by modifying the traditional two-component resist system. These compositions are generally composed of two main functional components: a polymer having acidic functional groups to render the polymer soluble in alkaline developer wherein some or all acidic functional groups are protected with acid labile protective groups so that the polymer is insoluble in alkaline developer, and an acid generator capable of generating an acid upon exposure to high-energy radiation. However, the activity of the acid generated by the acid generator must be controlled in order to attain a high resolution. To this end, a basic compound must be added as an additional component.
Base resins comprising an aromatic skeleton are kept away in the ArF and F2 lithography since they exhibit substantial absorption to ArF excimer laser and F2 laser radiation. These resins are used as a main component in KrF excimer laser and EB lithography, since the aromatic skeleton has high etch resistance and a phenolic hydroxyl group serves as the adhesive group to the substrate to provide good physical properties. For the EUV on which development works are concentrated as the next generation light source, there is a strong possibility of using a resin comprising an aromatic skeleton as the matrix material.
Of the polymers comprising an aromatic skeleton, a polymer comprising recurring units of 4-hydroxystyrene is most commonly used so far. This polymer has a phenolic hydroxyl group of weak acidity within the recurring unit while this functional group exhibits good adhesion to the substrate as well as solubility in alkaline developer. If the polymer is combined with protection of the phenolic hydroxyl group with an acid labile protective group, or with (meth)acrylic recurring units protected with an acid labile protective group, then a switch of solubility in alkaline developer can be triggered by an acid catalyst. Based on this concept, a number of polymers have been proposed. In JP-A 2008-95009, for example, a rectangular pattern having a line width of 70 nm is formed.
On the other hand, recurring units of (meth)acrylic acid exhibit insignificant absorption near wavelength 200 nm if the substituent group is alicyclic, and various copolymers can be readily prepared through copolymerization. Many polymers comprising recurring units of (meth)acrylic acid are used as the resist adapted for exposure to ArF excimer laser light. Those (meth)acrylic acid recurring units whose ester substituent group has an aromatic skeleton, despite more absorption near wavelength 200 nm, exhibit not only high etch resistance, but also have a tendency of displaying a reduced line edge roughness upon pattern formation. Their application to the EB or EUV lithography is proposed in JP-A 2007-114728.
In the course of development of the foregoing resist compositions, many modifications are made on various materials to improve the resist performance. Many modifications of the basic compound for inhibiting acid diffusion have been reported. For example, in conjunction with the resist composition for use in the ArF immersion lithography involving exposure of a resist film to ArF excimer laser light in a setup that a water layer is formed on the resist film, JP-A 2008-133312 proposes to use a polymer having a basic compound bound thereto in order to prevent the basic compound from migrating and diffusing into the water phase in contact with the resist film to alter the resolution of the resist surface region.
As an exemplary polymer endowed with a nitrogen-containing partial structure, a resist composition using a heterocycle-bearing polymer is disclosed in JP-A 2009-86310 although this is not for the purpose of restraining acid diffusion.
Citation List                Patent Document 1: JP-A 2008-95009 (U.S. Pat. No. 7,501,223)        Patent Document 2: JP-A 2007-114728 (U.S. Pat. No. 7,449,277)        Patent Document 3: JP-A 2008-133312        Patent Document 4: JP-A 2009-86310 (US 2009087789, EP 2042925)        Patent Document 5: JP-A H07-319155        Patent Document 6: JP-A 2009-263487 (US 2009269696, EP 2112554)        Patent Document 7: JP-A 2008-102383 (US 2008096128)        Patent Document 8: JP-A 2004-115630        Patent Document 9: JP-A 2005-008766 (US 2004260031)        